Cavity resonator structure and tube employing the same



Jan. 20, 953 P SPENCER 2,626,372

CAVITY RESONATOR STRUCTURE AND TUBE EMPLOYING THE SAME Filed 00T.. 7, 1950 lll/lll] /M/f/Vra/i Pflfcy L. SP5/vom Patented Jan. 20, 1953 UNITED sr..fififl11s PATENT oFF-LCE CAVITYRESONTOR STRUCTURE "AND :TUBEEMPLOYING THE'SAM'E Percy L.-Spencer, West Newton, Mass., assigner to :Raytheon Manufacturing Company, s Newton, .Mass,., `a corporation of Delaware Application' October "7, 1950, Serial'1No.f-189',018

:4 Claims. ,@1 This inventionrelates tcrcavity resonator vstructures and to :electron-discharge@devices of the type, for example, magnetrons, employing such structures.

It is well known that tubes designed kfor :the l generation of electricalcoscillations inthe micro- Wavev region of: the electromagnetic. spectrum. and incorporating :multiple Nfrequency-deterrnining cavity resonators for this'purposeihavepa tendency YVto roscillatev at :modes other than y the .desired mode. The :undesiredmodes represent ,a waste of: energy and. itl has heretofore been proposed to suppress fthembyza method .known as strapping.

This consists, broadly speaking, :.ofinterconnesting, by low-impedancemeans, pointsinthe high-capacitance regions :of the multiple cavity resonators intended during oscillation -simultaneously to .be of like phase.

fI-Iowever, due to .space limitations, strapping is not always` feasible. Furthermore, and particularly in high power-tubes,thestrappingmeans isxsometimes called zupon to carry excessively highcurrents.

It is also Well .knownuthatc in .tubes of the type above referred to, variations inv theexternal -load havera marked pulling effect upon the frequency for'which the tube is designed.

It is, therefore, amongwi'lher objects of thel present invention to-zeliminate r the foregoing disadvantages by providing accavityy resonatoriA structure which may be conveniently.used,:for;exam ple,.in `electron-discharge devices :of the magnetron type, 'and which isuccessfullyfsuppresses spurious oscillations without. the necessity, of any strapping.

It is another object of the presentainvention to provide a cavityl resonator structure which fisso constructed as to minimizethe pulling-veffectof variations in the external load.

Itis avfurther objectof theA present invention to providea cavityv resonator structure which may be employed as aforesaid, and which is simple in construction and easy and economical to "fabricate and assemble.

These, and other objects, which Will'become more apparent as the detailed description ofthe present invention progresses,are attained, briefly, in the following manner.

The cavity resonator structure ofthe present invention includes a plurality of conductive members each of Whichpartially encloses aregicn of space and, preferably, is-of a substantially resonant electrical length, peripherally about said region of space. 'If desired, some of said conductive :members :can :be of fadiierent Y resonant electrical lengthsgasgare .thezelementslof; the; cavity Vresonator structures `of the `So-Called rising sun type. Each'ofsai'd conductive members has at least zone portion;thereof extending intothe region; of space enclosed. by the immediatelygadjacent conductive,- member. Prefer.ab1y,the: conductive members .are a of 4 substantially Ufshaped transverse section, and are .eachprovidedgwith longitudinally slotted portions which ,;stradd1e oppositely longitudinally slottedfr portions. of immediately adj acent conductive `mem-bers.

When .incorporated in an electron-,discharge device, .for example, 4of the magnetronitvpe, the cavity resonator structure of .the `present linvention, may ,constitute theranode of said. device, and the above referred `to conductive members thereof may bel circumferentiallyA disposed to deiine a--central space receptive of the cathodebi said device- In the followingspecification there shall )be described, and in the accompanyingdrawingfshown, illustrative embodiments of thercavity.- resonator structure, .and tube employing the.,same, of .the present invention. lt,k is, however, to 4.be .clearly .understood that thefpresentinvention not .to

be limited tothesexact details'hereinshown and described for purposes of c illustration.only, in-

asmuch as changestherein .may bemade with-y out.. the exercise of inventionandwithinthe true spirit andrscope of the,claimslheretoappended.

vIn said drawing:

Fig. rv1 isa longitudinal sectional view taken substantially throughv the center of a magnetron incorporating a cavity resonator made ,accordance with thepresent invention Fig. 2 is atransverse sectional View taken von line 2-"2 ofFigil;

VVFigf3 is a fragmentaryperspective vieWof a portion of the anode of said magnetron; and

AFigli is an enlarged'furtherffragmentaryperspective View of 'the same showing more clearly the mannerinwhich .the conductive members above referred to are intercoupled.

Referring now, more. in detailto the aforesaid illustrative embodiment of the present invention, with particular reference. to the'drawingjillustrating the same, the numeral Il generally 'designates an electron-discharge device ofthe magnetron type. Said device comprises ,an anodeA structure Il, a cathode structure l2, andrmagnetic means I3Y for establishing a magnetic'eld' between .said anode and cathode -structures, .in a .direction transverse to theelectro n pathltherebetween.

"In the device shown,the anode structure'll' includes a hollow cylnidrical body I4, made of highly conductive material, such as copper, the inner wall of said body being provided, in the longitudinal mid-region thereof, with a multiplicity, here shown as ten, of shallow arcuate depressions I5. Secured in each such depression I5, and extending radially inward from the body I4, is a substantially U-shaped conductive member I6, each such member I6 partially enclosing a region of space I1 in advance thereof and being of a substantially resonant electrical length, for example, a half wave length, peripherally about said region of space. Each conductive member I6 thereby constitutes a cavity resonator.

As best seen in Fig. 4 of the drawing, each conductive member I6 is provided, adjacent the yoke portion thereof, with a longitudinal slot I8, adjacent conductive members having their respective slots oppositely disposed, whereby the arm portions I9 of said members may straddle each other and extend into the region of space I1 of the immediately adjacent member.

This arrangement affords tight inductive coupling between the individual cavity resonators provided by the multiple conductive members I6, as a result of which the structure tends to lock in at the desired mode of oscillation, namely, the nmode, in which successive arm portions I9 of each member I6 are 180 out of phase with respect to each other, the frequency of this mode being determined, primarily, by the electrical length of said members I6, as above stated, peripherally about the space enclosed thereby.

Furthermore, the aforesaid tight inductive coupling between the individual cavity resonators reduces to a negligible amount the frequency pulling effect of external loading conditions.

The anode structure |I is closed at its ends, for example, by end plates 20 and 2|, with the junctions between the cylindrical body I4 of said structure, and said plates 20 and 2|, being hermetically sealed, as at 22.

The conductive members I6 are, preferably, circumferentially disposed to provide a central space 23 which is receptive of the cathode structure I2. The latter, which is coaxial with the anode structure II, includes a cathode sleeve 24, conventionally made of nickel, or the like, provided with a reduced portion 25 the length of which, preferably, is coextensive with the longitudinal dimension of the arm portions I9 of the conductive members I6, said reduced portion 25 being provided with a highly electron-emissive coating, for example, of the well known alkalineearth metal oxide type.

In order properly to support the cathode sleeve 24 with respect to the arm portions I9 of the conductive members I6, said sleeve may be reduced, as at 26, to fit into an elongated, electrically conductive tubular member 21 having, at its outer end, a ferrule 28 closed by a glass seal 29. Said seal, together with one or more glass beads 30 disposed within said tubular member 21, supports a lead-in conductor 3| which passes through said tubular member and has its upper end connected, as at 32, to one terminal of a cathode heating filament 33. The other terminal of said filament may be connected, as at 34, to the cathode sleeve 24.

In order to convey current to the filament 33, the lead-in conductor 3| is connected by a conductor 35 to one terminal of a suitable source of voltage (not shown), the other terminal of said source of voltage being connected by a conductor 36 to a heat dissipating member 31 fixed upon the lower end of the tubular member 21.

In order to properly support the cathode structure I2, and insulate the same from the anode structure I I, the tubular member 21 may have xed thereto a cup-like bushing 38 sealed into one end of a glass tube 39, the other end of said glass tube having sealed therein a tubular bushing 4l), in turn, secured to a tubular pole piece 4| constituting one of the components of the magnetic means I3.

Said pole piece 4| may be hermetically sealed, as at 42, into the end plate 2| and be provided with a central bore 43, whereby the cathode structure I2 may enter the device.

Another pole piece 44, provided with a recess 45 receptive of the upper end of the cathode structure I2, may be hermetically sealed, as at 46, into the end plate 20, said pole piece and the pole piece 4I being iixed, for example, at the opposite ends of a horseshoe magnet 41 (only partially shown), whereby an appropriate magnetic eld may be established, as previously indicated, between the anode structure and cathode structure I2.

By suitably heating the cathode, and applying a power potential difference between said cathode and the anode, the device can be made to generate electrical oscillations of a wave length determined by the capacitance and inductance built into said device as a function of the geomtry thereof, and more especially, of the dimensions of the above referred to cavity resonators defined by the conductive members I6 of the anode structure.

In order to extract power from the device, a loop 48 may be introduced into one of the cavity resonators provided by the conductive members I 6, said loop coupling with the magnetic component of the generated electrical oscillations. While not specifically shown, the loop may be connected to the inner conductor of a coaxial transmission line, the outer conductor of said transmission line being connected to an outlet pipe 49. It is to be understood, of course, that the inner and outer conductors of the transmission line will have an appropriate hermetic seal therebetween so as to maintain the usual vacuum within the anode structure II.

This completes the description of the aforesaid illustrative embodiments of the present invention. It will be noted from all of the foregoing that there has been provided a cavity resonator structure which is especially useful in electron-discharge devices of the magnetron type, which cavity resonator structure includes multiple cavity resonators which are tightly inductively coupled, whereby spurious oscillations are suppressed without the necessity of the strapping arrangements which have heretofore been proposed for this purpose and external loading conditions have very little pulling eifect on the frequency at which the device is intended to operate. It will also be noted that construction of the present invention is simple and may be economically fabricated and assembled.

Other objects and advantages of the device of the present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

l. A cavity resonator structure comprising: a plurality of strap-like conductive members each of which is of substantially U-shaped transverse section; each of said conductive members having longitudinally slotted portions straddling oppositely longitudinally slotted portions of the irnmediately adjacent conductive members and eX- tending into the regions of space enclosed by said immediately adjacent conductive members.

2. An electron-discharge device comprising: a cathode; an anode structure spaced from and surroundingr said cathode; said anode structure including a plurality of circumferentially disposed conductive members dening a central space receptive of said cathode; each of said conductive members partially enclosing a region of space; and each of said conductive members having portions thereof extending into the regions of space enclosed by the immediately adjacent conductive members.

3. An electron-discharge device comprising: a cathode; an anode structure spaced from and surrounding said cathode; said anode structure including a plurality oi identical, circumferentially disposed conductive members defining a central space receptive of said cathode; each of said conductive members partially enclosing a region of space; successive conductive members having oppositely slotted portions which mutual- PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,144,222 Hollmann Jan. 17, 1939 2,546,773 Nelson Mar. 27, 1951 FOREIGN PATENTS Number Country Date 611,732 Great Britain eeee Nov. 3, 1948 

